1. Field of the Invention
The present invention relates to a fuel cell system capable of recovering and recycling water produced in a cathode electrode, and more particularly, to a fuel cell system which transfers water produced in a catalyst layer of a cathode electrode to an electrolyte polymer membrane through a gas diffusion layer in order to recycle water.
2. Discussion of the Related Art
In general, a fuel cell system is a power generating system that generate electricity by electrochemical reaction between hydrogen contained in a hydrogen containing fuel and oxygen contained in an oxidant. Such a fuel cell system includes an electric generator to generate electricity through the electrochemical reaction between the hydrogen and oxygen, a fuel feeder to supply the hydrogen containing fuel to the electric generator, and an oxidant feeder to supply the oxidant to the electric generator.
The electric generator includes a unit cell having a membrane electrode assembly. The membrane electrode assembly includes an electrolyte membrane having selective ion permeability, and anode and cathode electrodes provided on opposite sides of the electrolyte membrane. In the anode electrode, carbon dioxide, hydrogen ions and electrons are produced by a reaction between the hydrogen containing fuel (e.g., methanol) and water, and the hydrogen ion is transferred to the cathode electrode through the electrolyte membrane. In the cathode electrode, the hydrogen ions, the electrons transferred through an external circuit, and oxygen are reacted to produce water.
When water produced in the cathode electrode is not smoothly discharged, oxygen from the outside is not introduced, so that the power generation efficiency of the fuel cell system deteriorates. Technology has been proposed to recycle water produced in the cathode electrode.
Japanese Patent First Publication No. 2004-152561 relates to a direct methanol fuel cell that includes a water recovering unit to recover some of the water produced from an air electrode and discharge the remainder of the water to the outside; and a mixer to mix water recovered by the water recovering unit with an aqueous methanol solution supplied from a fuel storage tank.
In Japanese Patent First Publication No. 2005-527063, as shown in FIG. 5 of the accompanying drawings, a fuel cell system has at least one thin membrane electrode assembly 16 in communication with a water recovering/recycling system 64 through a water recovering/recycling channel 53.
However, a structure for effectively recovering water from the air electrode is not included in the above-described patent applications.
In Korean Patent First Publication No. 2002-0019588, as shown in FIG. 6 of the accompanying drawings, a fuel cell has a gas diffusion layer 24 adjacent to a cathode 22 and including a first layer 241 contacting the cathode 22; and a second layer 242 thicker than the first layer 241 and having a surface along which oxidant gas flows, thereby maintaining the wettability and the gas diffusibility of a solid polymer membrane within a cell. However, because such first and second layers are provided separately, a production cost of the gas diffusion layer increases.
In U.S. Pat. No. 6,660,423, as shown in FIG. 7 of the accompanying drawings, a fuel cell system includes a membrane electrode assembly 16 having a hydrophilic thread 30 to absorb water produced in a cathode electrode 22, and a water recovering/circulating channel 58 communicating fluid to the hydrophilic thread 30. However, because such channel is separately provided for recovering water from the cathode electrode, cost and time for producing the fuel cell system are increased.